It is well known to use switched mode power supplies (SMPSs) in mobile telephones. An SMPS rapidly switches a power transistor between saturation and cutoff with a variable duty cycle whose average leads to the desired output voltage. The resulting rectangular waveform is low-pass filtered with an inductor and capacitor. The main advantage of SMPSs is greater efficiency because the switching transistor dissipates little power in the saturated state and the off state compared to the semiconducting state. Other advantages include smaller size and lighter weight and lower heat generation from the higher efficiency. Disadvantages include complexity, the need to block high amplitude, high frequency energy, and a ripple voltage at the switching frequency and harmonic frequencies thereof.